Add even more debug messages

The UFO game is trying to render stuff at absurd positions. This makes
my rendering going way outside its jurisdiction on the Chip-8 screen. I
represent its matrix as linear array of 2048 pixels (64 * 32). The game
is trying to render pixels at positions like 8601 and this causes
segmentation faults.

Now, obviously the game has been around for 20+ years and is working
properly. I probably have some problems with the opcodes dealing with
the registers, for me to even try to draw such coordinates.